Method of and apparatus for treating quicksilver ores



NOW 1931- L. H. DUSCHAK ET AL 1,332,006

METHOD OF AND APPARATUS FOR TREATING QUICKSILVER ORES Filed July 19, 1927 INVENTOR. KW J4 09 WW 7 BY 16% azz/M d fy iiif; W

ORNEYS.

Patented Nov. 17, 1931 UNITED STATES PATENT, orrlcs LIONEL H. DUSCHAK AND CLIFFORD G. DENNIS, OF SAN'FRANCISCO, CALIFORNIA, AS-

SIGNORS OF ONE-HALF TO GOLDEN GATE GOLD MINING CO. AND ONE-HALF TO HOMESTAKE GOLD MINING CO., BOTH OF SAN FRANCISCO, CALIFORNIA, AND BOTH CORPORATIONS OF, CALIFORNIA METHOD OF AND APPARATUS FOR TREATING QUICKSILVER ORES Application filed July 19, 1927. Serial No. 206,874.

This invention relates to the treatment of quicksilver ores. i

In the treatment of quicksilver ores on a large scale the common'practice is to roast these ores either in a Scott furnace or a rotary kiln similar to that used for cement burning, and then cool the quicksilverdaden gases to condense the quicksilver vapor. Quicksilver ores are not in general self-roasting; that is, they do not contain sulphur or other combustible matter in sufficient quantity to supply the fuel requirements of the roasting operation. It is therefore necessary to supply heat through the combustion of'fuels such as wood, coal or oil. With either of the above types of furnace, countercurrent .firing is commonly used. That is, the hot gases from the combustion chamber flow in a direction opposite to the direction of movement of the ore.

When this regular practice is applied to quicksilver ores containing either elemental sulphur or more than asmall per cent of sulphides such as pyrite which evolve sulphur vapor when heated, difiiculty is encountered owing to the volatilization of elemental sulphur in the furnace and the union of this sulphur with the quicksilver vapor in the condenser. vapor and mercury vapor may be formulated as follows:

Hg+ S =HgSj When conditions are such that this reaction takes place. in the condenser system, the product obtained from the condenser consists in'part at least of synthetic mercury sulphide which must be subjected to further treatment before metallic mercury is obtained. This not only involves addiional expense in operation, but is undesirable because of the metal values tied 'up in material requiring re-treatment, the possible loss of material in handling, and because of the health hazard involved in the treatmentof so-called mercurial soot The object of our invention is to overcome the difficulties above noted, in the treatment of sulphur-bearing quicksilver ores by roasting the ore in sucha way that the Sulphur The reaction between sulphur.

is completely burned. This is accomplished by maintaining an oxidizing atmosphere throughout the roasting furnace and conduct- ,ing the roasting operation in such a way that any sulphur vapor evolved from the ore will be brought in contact with an excess of oxygen at a temperature sufficient to promote complete reaction between the sulphur vapor and the oxygen. The process may be con- Fig. 2 shows a similar view of the rearward portion.

Fig. 3 shows a sectional view taken on the line IIIIII of Fig. 2.

This apparatus includes a rotary kiln A, I

with an ore feeder B and an oil or gas'burner C. Any fuel may be used in this connection, the essential point being. that the firing and the charging of the ore are done at the same end of the kiln; that is, the hot gases of combustion and of the ore travel in the same direction through the kiln. The hot ore, when completely roasted, is discharged from the kiln into a rotary cooler D, where the roasted ore is cooled by a stream of air. heated by contact with the roasted ore is delivered to the feed end of the kiln, through pipe E, thus not only regenerating useful heat, but promoting the rapid combustion of the fuel and rapid heating up of the cold ore charged into the furnace.

At the feed end, the kiln may be equipped with deflecting veins F to move the ore forward rapidly into the kiln and prevent it "travel in the same direction through the furnace. With this method of operation any sulphur vapor which may escape from the ore is forced to pass through a long, hot zone in which the combustion of the sulphur is completed before the gases leave the furnace.

The, air thus Gil A damper G is provided for regulating the amount of air admitted to the furnace, and thereby an excess of oxygen may be maintained in the furnace atmosphere. In the presence of this excess of oxygen the sulphur vapor is completely oxidized to form sulphur dioxide and some sulphur trioxide. Neither of these substances reacts to any appreciable I extent with mercury vapor or interferes with its condensation. Hence, when the gases resulting from this operation are cooled the mercury vapor condenses in metallic form and no formation of mercurial soot takes place. I

Adjoining the kiln at the discharge end is a dust chamber H. A hopper I for receiving the calcined ore is provided in'the bottom of the dust chamber next to the kiln. The central part of the dust chamber is filled with a brick checker work J for the purpose of thoroughly mixing the gases leaving the kiln and providing a hot contact surface for completing the oxidation of any trace of sulphur vapor which may escape unburned from the kiln. A second hopper K is provided in the bottom of the dust chamber in the end remote from the kiln for collecting any coarse dust which may settle from the gas stream.

Owing to the method of parallel firing employed, the temperature of the furnace gases entering the dust chamber is much higher than the temperature of gases ordinarily leaving a quicksilver roasting furnace. This necessitates special provision for cooling the gases and condensing the mercury vapor. The first stage of cooling is effected in a set of thin-walled metal pipes,

one of which is shown at L. From thesecooling pipes thefurnace gases pass to an electrostatic precipitator M where the Cottrell process is employed for removing the barren dust conveyed from the furnace by the gas stream.. The removal of dust from quicksilver furnace gases has always been a problem in quicksilver metallurgy, more particularly when rotary kilns or other types of mechanical furnaces are employed. The subsequent cooling of the gases and condensing of the mercury vapor. is greatly simplified by employing a special device for freeing the furnace gases from dust.

quicksilver from it, the danger of the loss of quicksilver through leakage is multiplied, and a certain amount of metal is unavoidably retained in cracks, crevices, etc. of the system.

We overcome these difficulties in our process by cooling the gases and collecting the condensed quicksilver in three compact units which require relatively little floor space, and which may be easily and quickly inspected at any time. collecting units are shown in Fig. 2.

The first of these units is a spray tower N, in which the hot gases are mixed with finely divided water mist delivered by high pressure spray nozzles O. Baliles P are provided in this tower to insure thorough mixing of the Water mist with the gas stream. In this unit the cooling is effected chiefly through the evaporation of water, the gases leaving the bottom of this tower having a temperatureapproximately that of the boiling point of water. In the next unit Q the gases now laden with considerable water vapor are brought in contact with a multiplicity of water-cooled metal pipes B. These pipes are arranged in horizontal layers, those in one layer being opposite the openings between the pipes in the layers immediately above and immediately below. This staggered arrangement of the pipes promotes turbulence in the gas,

stream and insures intimate contact between the gases and the water-cooled pipes. In this second-unit the gases are cooled to approximately 30 0., a temperature at which only a minute amount of mercury will remain in.

the vapor state.

A particularly high efficiency in cooling is achieved by this method of spraying the gases with water in one unit and condensing the resulting water vapor in a second unit.

The reason for this high efiiciency is found in the fact that when heat is transferred to a cold surface by a vapor which condenses, the

rate of heat transferred is much higher than when the heat is conveyed by a non-condensing gas. In this method of cooling the sensible heat of the hot gases is first converted, in part, into the latent heat of water vapor and this latent heat then removed by condensing the water vapor on a cold metal surface.

The gas stream, after being cooled, is conveyed to a second Cottrell precipitator S where any mercury mist remaining in suspension'is collected. From this second Cottrell precipitator the gas stream passes to an exhauster T and thence to the stack U.

The plant illustrated herewith in describing the process employs a rotary kiln as the roasting furnace. However, the same principle of parallel firing can be applied to other types of roasting'furnace, and this invention is not limited to any particular type of furnace, except that it shall be of the parallel firing type.

The main features and advantages of the These cooling and above process are: (a) the parallel firing of the furnace; that is, causing the ore and furnace gases to move through the furnace in the same direction; and (b) the method employed for the final cooling of the gases; that is, spraying with Water and then condensing the Water vapor on a cold metal surface.

Having thus described our invention, What we claim and desire to secure by Letters Patent is:

1. In the treatment of quicksilver ores, the step of continuously feeding the ore into one end of a roasting furnace and discharging it at the opposite end, and directing hot gases of combustion through the furnace in the direction of movement of the ore.

2. In the treatment of quicksilver ores, the step of continuously feeding the ore into one end of a rotary furnace and discharging it at the opposite end, and directing a flame through said furnace in the direction of movement of the ore.

3. In the treatment of quicksilver ores, the step of continuously feeding the ore into one end of a rotary furnace and discharging it at the opposite end, directing a flame through said furnace in the direction of movement of the ore, and thence moving the hot ore through a cooler and directing the hot air from the cooler into the feed end of the furnace.

4. In the treatment of quicksilver ores in a roasting furnace, a method of abstracting heat from the hot furnace gases Which consists of first spraying the gases With Water in order to convert sensible heat into latent heat, and passing the gases containing the Water vapor through a separate condensing chamber.

CLIFFORD G. DENNIS. LIONEL H. DUSGHAK. 

